The present invention generally relates to a liquid material dispensing apparatus and nozzle and, more specifically, to an apparatus and nozzle for dispensing controlled patterns of liquid adhesive strands or filaments.
Many reasons exist for dispensing liquid adhesives, such as hot melt adhesives, in the form of a thin filament or strand with a controlled pattern. Conventional patterns used in the past have been patterns involving a swirling effect of the filament by impacting the filament with a plurality of jets of air. This is generally known as controlled fiberization or CF(trademark) in the hot melt adhesive dispensing industry. Controlled fiberization techniques are especially useful for accurately covering a wider region of a substrate with adhesive dispensed as single filaments or as multiple side-by-side filaments from nozzle passages having small diameters, such as on the order of 0.010 inch to 0.060 inch. The width of the adhesive pattern placed on the substrate can be widened to many times the width of the adhesive filament itself. Moreover, controlled fiberization techniques are used to provide better control of the adhesive placement. This is especially useful at the edges of a substrate and on very narrow substrates, for example, such as on strands of material such as Lycra used in the leg bands of diapers. Other adhesive filament dispensing techniques and apparatus have been used for producing an oscillating pattern of adhesive on a substrate or, in other words, a stitching pattern in which the adhesive moves back-and-forth generally in a zig-zag form on the substrate. These dispensers or applicators have a series of liquid and air orifices arranged on the same plane.
Conventional swirl nozzles or die tips typically have a central adhesive discharge passage surrounded by a plurality of air passages. The adhesive discharge passage is centrally located on a protrusion which is symmetrical in a full circle or radially about the adhesive discharge passage. A common configuration for the protrusion is conical or frustoconical with the adhesive discharge passage exiting at the apex. The air passages are typically disposed at the base of the protrusion. The air passages are arranged in a radially symmetric pattern about the central adhesive discharge passage, as in the protrusion itself. The air passages are directed in a generally tangential manner relative to the adhesive discharge passage and are all angled in a clockwise or counterclockwise direction around the central adhesive discharge passage.
Conventional meltblown adhesive dispensing apparatus typically comprises a die tip having multiple adhesive or liquid discharge passages disposed along an apex of a wedge-shaped member and air passages of any shape disposed along the base of the wedge-shaped member. The wedge-shaped member is not a radially symmetric element. Rather, it is typically elongated in length relative to width. The air is directed from the air discharge passages generally along the side surfaces of the wedge-shaped member toward the apex and the air impacts the adhesive or other liquid material as it discharges from the liquid discharge passages to draw down and attenuate the filaments. The filaments are discharged in a generally random manner.
Meltblown style dispensers provide a convenient and cost effective platform for discharging a liquid material, such as hot melt adhesive or another material. The air discharge passages of meltblown dispensers are typically arranged symmetrically on either side of and at the base of the wedge-shaped member, i.e., in a different plane than the liquid discharge passages to attenuate the filaments. However, effectively controlled swirling of adhesive filaments from this style of applicator has not been developed to date. It would therefore be desirable to provide a meltblown style dispenser for producing a controlled swirling of the liquid filaments.
The present invention provides a meltblown style applicator with the capability of producing a controlled swirling of the liquid filament. This results in repeatable filament orientation with improved edge control. Further, the invention provides a predictable relationship between a specific geometric configuration of liquid and air discharge passages and the resulting pattern width and frequency. Thus, the nozzle configuration can be controlled to give a tighter, high frequency filament pattern or a more open, lower frequency filament pattern.
The present invention generally provides a liquid dispensing module or applicator for discharging at least one liquid filament onto a moving substrate with a swirled pattern. The dispensing module includes a dispenser or module body for receiving pressurized liquid and air and a nozzle is coupled to the module body. The nozzle comprises a nozzle body having a first side and a second side with the first side coupled to the module body and including a liquid supply port and an air supply port coupled with respective liquid and air supply passages of the module body. In the preferred embodiment, the first and second sides are respectively located on perpendicular planes of the nozzle body, but other configurations may be used as well. A wedge-shaped member is located on the second side of the nozzle body and includes a base, an apex and a pair of side surfaces converging toward the apex. A liquid discharge passage extends along an axis through the apex of the wedge-shaped member. The liquid discharge passage communicates with the liquid supply port of the nozzle body. The wedge-shaped member extends in a radially asymmetrical manner around the liquid discharge passage. The nozzle body further includes a plurality of air discharge passages positioned adjacent the base of the wedge-shaped member. At least two of the air discharge passages are positioned adjacent each of the side surfaces and each of the air discharge passages is angled in a direction generally toward the liquid discharge passage. Each air discharge passage is also offset from the axis of the liquid discharge passage.
In the preferred embodiment, the nozzle body includes four of the air discharge passages positioned in a generally square pattern about the liquid discharge passage. Two of the air discharge passages are positioned at the base adjacent one of the side surfaces and two of the air discharge passages are positioned at the base adjacent the other of the side surfaces. Each of the air discharge passages is offset by the same distance from the axis of the liquid discharge passage. The air discharge passages positioned at diagonally opposed corners of the square pattern are symmetrically positioned relative to the liquid discharge passage. Each of the air discharge passages are offset from the axis of the liquid discharge passage by a distance at least equal to the radius of the liquid discharge passage. The wedge-shaped member is preferably formed integrally with the nozzle body, such as through extrusion or machining techniques. Especially when dispensing hot melt adhesive materials, the liquid discharge passage has a diameter of between about 0.010 inch and about 0.060 inch and the air discharge passages are each offset from the axis of the liquid discharge passage by a minimum distance of about 0.005 inch to about 0.030 inch up to a maximum of about 0.060 inch.
The inventive concepts apply to dispensing modules having one or more sets of the liquid and air discharge passages. For many applications, it will be desirable to provide a nozzle having multiple side-by-side sets of liquid and air discharge passages with each set configured as described above. Each set may be arranged with respect to separate wedge-shaped members or multiple sets of liquid and air discharge passages may be arranged along the same wedge-shaped member. In each case, a desirable swirled liquid filament pattern is achieved and, moreover, due to the unique configuration of air and liquid discharge passages on opposite sides of a radially asymmetrical wedge-shaped member, a nearly linear relationship exists between the offset dimension, which is defined between the air discharge passages and the axis of the liquid discharge passage, and the resulting pattern width and frequency. As a result, different configurations of the air and liquid discharge passage may be made with precisely predictable results in terms of both swirled pattern width perpendicular to the substrate movement and oscillation frequency parallel to the movement of the substrate of the swirled pattern.
These and other features, objects and advantages of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description, taken in conjunction with the accompanying drawings.